1. Field of the Invention
The present invention relates to a positive photoresist composition and a method of patterning a resist thin film for use in inclined implantation. More specifically, it relates to a highly sensitive positive photoresist composition that is used in photolithography using i-line (365 nm) and specifically advantageously in an inclined implantation process using a very thin resist film about 0.1 to 0.5 xcexcm thick, as well as to a method of patterning a resist thin film for use in inclined implantation process using the positive photoresist composition.
2. Description of the Related Art
Photoresist compositions each containing an alkali-soluble resin and a quinonediazido-group-containing compound have satisfactory definition, sensitivity, etching resistance and thermal resistance in photolithography process using i-line (365 nm) and therefore have been applied to practical use in fabrication of semiconductor devices and liquid crystal devices.
Such resist patterns having a size smaller than the wavelength of exposing light have been believed to be hardly formed by photolithography without deteriorating the above properties. However, fine resist patterns of about 0.35 xcexcm, smaller than the wavelength of i-line, can now be formed as a result of improvements in materials, process conditions and exposure techniques.
With increasing diameters of silicon substrates for semiconductors and glass substrates for liquid crystal display devices, increasing demands have been made on positive photoresist compositions with higher sensitivity to improve throughputs. Improvements in conventional positive photoresist compositions each containing an alkali-soluble resin and a quinonediazido-group-containing compound have therefore been proposed.
For example, Japanese Patent Laid-Open No. 3-107160 discloses a resist composition containing an alkali-soluble hydrogenated phenol resin, a 1,2-naphthoquinonediazido-5-sulfonic acid ester as a photosensitive acid generator, and a compound having an acid-decomposable group.
However, the resist composition must be exposed to excimer laser light and thus invites high production cost. The resist composition is readily deactivated upon contact with a basic substance in the air to vary its sensitivity and is thereby insufficient in post-coating delay (PCD; time interval between coating process and exposure process) stability and post-exposure delay (PED; time interval between exposure process to post-exposure baking (PEB) process) stability. In short, the resist composition is insufficient in xe2x80x9cstability of latent image before development.xe2x80x9d
Japanese Patent Laid-Open No. 3-249654 discloses a photosensitive composition containing an alkali-soluble novolak resin, a 1,2-naphthoquinonediazido-4-sulfonic acid ester as a photosensitive acid generator, and a compound having an acid-decomposable group.
However, the photosensitive composition readily invites insoluble matters to form during storage and must have higher definition and sensitivity.
Japanese Patent Laid-Open No. 6-130665 discloses a photosensitive composition containing an alkali-soluble novolak resin, a 1,2-naphthoquinonediazidosulfonic acid ester as a photosensitive acid generator, a compound having an acid-decomposable group, and a ketone solvent.
However, the photosensitive composition must be exposed to excimer laser light and thus invites high production cost.
Japanese Patent Laid-Open No. 6-202320 discloses a photosensitive composition containing an alkali-soluble novolak resin, 1,2-naphthoquinonediazido-4-sulfonic-acid ester of polyhydroxybenzophenone, and a compound having an acid-decomposable group.
However, the photosensitive composition readily invites insoluble matters to form during storage and must have higher definition and sensitivity.
Japanese Patent Laid-Open No. 8-220749 discloses a resist composition containing an alkali-soluble novolak resin, a 1,2-naphthoquinonediazido-5-sulfonic acid ester, a compound having an acid-decomposable group, and a photosensitive acid generator.
However, the resist composition readily varies in its sensitivity during storage and must have higher definition and sensitivity.
In addition, all the aforementioned compositions must be improved in their stability of latent image before development.
As a possible candidate to improve the stability of latent image before development, Japanese Patent Laid-Open No. 9-6001 discloses addition of a xe2x80x9cquencherxe2x80x9d material such as amines and organic carboxylic acids to a composition. The resulting composition, however, contains an increased number of components and thereby invites higher material cost.
Separately, an xe2x80x9cinclined implantationxe2x80x9d process is proposed in, for example, Japanese Patent Laid-Open No. 8-22965. In this process, an inclined semiconductor substrate having a patterned resist mask is subjected to ion implantation to thereby selectively implant dopant ions to a surface of the semiconductor substrate.
The process is believed to be effective for selective ion implantation into a small area of the substrate directly below the patterned resist or into side walls of holes disposed on the substrate.
When an ultrafine resist pattern of about 0.35 xcexcm is formed by the inclined implantation process, a patterned resist film serving as a mask must be very thin of about 0.1 to 0.5 xcexcm so as not to inhibit ion implantation.
However, when very thin resist films are formed using conventional positive photoresist compositions, the resulting very thin resist films cannot yield satisfactory latent images, are reduced in thickness in unexposed portions, invite large amounts of scum, or cannot yield patterned resists having a good shape.
In addition, the patterned resist films are exposed to elevated temperatures during implantation process and must have high thermal resistance. Accordingly, the resist films are subjected to xe2x80x9cpost-bakingxe2x80x9d heat treatment after development. The positive photoresist compositions for use in the implantation process must have sufficient thermal resistance to resist deformation of patterned resist films during post-baking.
Positive photoresist compositions for use in the inclined implantation process using a patterned resist thin film about 0.1 to 0.5 xcexcm thick must yield a patterned resist film with high definition and contrast and satisfactory shape, must have high sensitivity, yield less scum and have satisfactory stability of latent image before development and high thermal resistance.
Accordingly, an object of the present invention is to provide a positive photoresist composition that has highly improved sensitivity, definition, and stability of latent image before development, can yield a patterned resist thin film with high contrast, invites less scum and has satisfactory thermal resistance in an inclined implantation process.
Another object of the present invention is to provide a method of patterning a resist thin film for use in an inclined implantation process using the positive photoresist composition.
After intensive investigations, the present inventors have solved the problems of the conventional technologies.
Specifically, the present invention provides, in an aspect, a positive photoresist composition including:
(A) an alkali-soluble resin having a weight average molecular weight (Mw) in terms of polystyrene of from 1500 to 10000,
wherein a resin film 1 xcexcm thick prepared from the alkali-soluble resin completely dissolves in 2.38% by weight tetramethylammonium hydroxide (TMAH) aqueous solution at 23xc2x0 C. within ten seconds, the resin film being prepared by dissolving the alkali-soluble resin in a solvent to yield a solution, applying the solution to a substrate to yield a film, and drying the film at 110xc2x0 C. for 90 seconds;
(B) a quinonediazide ester represented by following Formula (I): 
wherein each of R1, R2, R3, R4, R5, R6, R7, and R8 is independently a hydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkyl group;
each of R9, R10, and R11 is independently a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms;
Q is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms, or Q is combined with R9 to form a cycloalkyl group containing 3 to 6 carbon members or a residue represented by following Formula (II): 
wherein each of R12 and R13 is independently a hydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkyl group; and
c is an integer of from 1 to 3;
each of Ds is independently a hydrogen atom or a 1,2-naphthoquinonediazido-5-sulfonyl group, where at least one of Ds is a 1,2-naphthoquinonediazido-5-sulfonyl group;
each of a and b is independently an integer of from 1 to 3;
d is an integer of from 0 to 3; and
n is an integer of from 0 to 3; and
(C) a phenolic compound having an acid-decomposable group and represented by following Formula (III): 
wherein each of R1, R2, R3, R4, R5, R6, R7, and R8 is independently a hydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkyl group;
each of R9, R10, and R11 is independently a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms;
Q is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms, or Q is combined with R9 to form a cycloalkyl group containing 3 to 6 carbon members or a residue represented by following Formula (IV): 
wherein each of R12 and R13 is independently a hydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkyl group; and
c is an integer of from 1 to 3;
each of Es is independently a hydrogen atom or a 1-ethoxyethyl group where at least one of Es is a 1-ethoxyethyl group;
each of a and b is independently an integer of from 1 to 3;
d is an integer of from 0 to 3; and
n is an integer of from 0 to 3.
The alkali-soluble resin (A) is preferably an alkali-soluble novolak resin containing equal to or more than 20% by mole of a m-cresol constitutional repeating unit in total phenolic constitutional repeating units and having a molecular weight distribution (Mw/Mn) of less than or equal to 6 wherein Mn is a number average molecular weight.
The positive photoresist composition may further comprise (D) at least one compound capable of absorbing light with a wavelength of about 365 nm.
Preferably, the 1-ethoxyethyl group substitutes for 30% to 100% by mole of total Es in the phenolic compound (C).
A resist film prepared from the positive photoresist composition preferably has a B parameter of from 0.2 to 1.0.
The positive photoresist composition of the present invention has highly improved sensitivity, definition, and stability of latent image before development, can yield a patterned resist thin film with high contrast, invites less scum and has satisfactory thermal resistance in the inclined implantation process.
The present invention provides, in another aspect, a method of patterning a resist thin film for use in inclined implantation process. The method includes the steps of:
(1) applying a solution of the positive photoresist composition to a substrate and drying the applied solution to thereby form a resist film having a thickness of from 0.1 to 0.5 xcexcm;
(2) selectively exposing the resist film through a mask;
(3) subjecting the exposed resist film to post-exposure baking;
(4) developing the resulting resist film with an aqueous alkaline solution to thereby dissolve and remove exposed portions of the resist film; and
(5) post-baking the resulting film.
By using the positive photoresist composition of the present invention, the method can pattern a resist thin film that can be advantageously used in the inclined implantation process.